This invention relates to the construction of an electrically heated vacuum furnace capable of reaching high temperatures on the order of 1500.degree. K to 3000.degree. K without the use of cooling water to protect the vacuum vessel. More specifically, the invention concerns the design of the vacuum vessel and the thermal insulation system, the thermal insulation system being designed to minimize heat transfer to the vacuum vessel, the vacuum vessel being designed to safely transfer all of this heat to the ambient air surrounding the vacuum vessel.